Background & Aims: Children with Crohn's disease are at risk for osteoporosis because of undernutrition, prolonged corticosteroid therapy, inflammatory process itself, inadequate calcium intake or absorption and vitamin D deficiency. The aim of this study is to address the effects of Crohn's disease and cumulative corticosteroid dose on calcium metabolism, efficiency of calcium absorption, calcitropic hormone levels and bone mineral density in preadolescent and adolescent girls. Methods: Seven female subjects (12 to 1 yrs. of age) have been enrolled. Patients are undergoing anthropometric assessment, pubertal staging, bone age radiography, and BMD assessment by dual energy 2-ray absorptiometry (DEXA) of the lumbar spine and total body. Clinical disease activity of CD is assessing by te Pediartic Crohn's Disease Activity Index (PCDAI). The cumulative corticosteroid dose (i grams) is calculating. Laboratory evaluations include serum levels of albumin, prealbumin, ionized Ca, phosphated, alkaline phosphatase, 25-hydroxyvitamin D [25-OHD], 1,25-dihydroxyvitamin D [1,25-(OH)xD], calcitonin, parathyroid hormone (PTH), estradiol, osteocalcin and interleukin-6, and urinary levels of N-telopeptide. We are measuring calcium absorption and urinary calcium excretion, using a dual-tracer, stable-isotope technique and thermal ionization mass spectrometry. Results: We have not completed this study yet. We hypothesize that the low bone mineral density reported in girls with Crohn's disease is related to disturbances in calcium metabolism.